[thumb one's nose] {v. phr.}
1. To hold one's open hand in front of one's face with one's thumb pointed at one's nose as a sign of scorn or dislike.
* /After Bob ran into the house he thumbed his nose at Tom through the window./
2. {informal} To look with disfavor or dislike; regard with scorn; refuse to obey. — Used with "at".
* /Betty thumbed her nose at her mother's command to stay home./* /Mary thumbed her nose at convention by wearing odd clothes./
Compare: LOOK DOWN ON.